<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    let num = +prompt("请输入一个数字：")
    let sum = 0
    for (let i = 1; i <= num; i++) {
      sum += i
    }
    console.log(`计算 1~${num} 之间的累加和为${sum}`)
  </script>
</body>
</html>